1. Field of the Invention
The present invention relates generally to the treatment of septic waste using tanks that contain liquid and other sewage materials in an underground buried location. In particular, the present invention relates to multiple compartment septic tank systems for processing septic waste in a multi-step process to provide a relatively clean effluent.
2. Description of the Related Art
Septic tanks for processing sewage materials have been known for many years and are generally manufactured from concrete, fiberglass reinforced resin materials, and rotationally molded plastics. Examples of concrete tanks are shown in U.S. Pat. No. 1,715,466 (Miller) and U.S. Pat. No. 5,544,460 (Fife). An example of a fiberglass reinforced septic tank is shown in U.S. Pat. No. 3,426,903 (Olecko). Molded tanks have become popular in recent years due primarily to their weight, cost and convenience. An example of a molded septic tank is shown in U.S. Pat. No. 4,961,670 (McKenzie et al.).
A conventional multi-step waste treatment system has been developed by MicroSepTec, Inc. of Laguna Hills, Calif. This conventional septic waste treatment system processes waste in a multi-step process resulting in a relatively clean effluent that is acceptable for irrigation or discharge into streams. This system uses modified standard septic tanks to hold the waste during processing. The physical installation of this system is much like the installation of a simple septic tank. However, this conventional system suffers from several disadvantages. For example, the tank quality is variable and frequently unsatisfactory, the tanks are large and awkward, and the tanks are not optimally designed to resist overburden and corrosion.
Fiberglass reinforced polyester (FRP) tanks are currently preferred in the industry because the installation and service of the special baffles required by the systems are simpler and more reliable than the alternative, which is roto-molded polyethylene (PE) septic tanks. Adding baffles or changing manways in PE tanks requires plastic welding methods, which are not reliable nor easily accomplished. FRP tanks, however, are largely made by handwork using open-molding methods. These methods are dirty and subject to variances in workmanship by individual craftsmen, which leads to an undesirable variance in quality.
The conventional septic tanks with all modifications are very large and heavy. They must be completely assembled in a factory under close supervision and then transported by truck to the installation site. Freight is very costly and limits the trade area that conventional tanks can be shipped from the point of manufacture. Further, when the tanks arrive at the site, an overhead crane is required to unload and place the tanks. This further increases the cost and creates scheduling problems, particularly where cranes are not readily available. Lastly, unloading and placing the tanks is a problem because FRP is prone to impact damage, which must be repaired at the site before installation can continue. Elimination of transportation, installation, and repair cost is important to improve the market acceptance of new waste treatment systems.
The current designs used by MicroSepTec are typical of plastic septic tank designs that evolved from reinforced concrete (RC) septic tank designs. With RC designs, the low material cost and high strength of RC permits tanks with large width and length and small height. This small height keeps the depth of the hole that must be dug at a minimum while still allowing the tank to receive wastewater by gravity flow. The RC strength easily supports the overburden. With FRP and PE tanks, the height must be increased and the width reduced, while the length can be increased, requiring a deeper and more costly hole. Generally plastic tank designs have included a rectangular base and a steeply arched top to minimize, distribute, and help carry the overburden load. Ribs are often used to strengthen such tanks. Some tanks, like those currently used by MicroSepTec, are simple cylinders with sufficient ribbing to support whatever load is not distributed to the sidewalls, which are supported by the side thrust of the supporting soil. All of these designs utilize extra materials to carry the overburden loads. The ability to reliably manage the overburden loads and avoid failures or leaks is important because such failures can damage the reputation of the manufacturer, violate sanitary ordinances, and result in costly compensation to customers.
The MicroSepTec system is expensive and expected by the customer to operate trouble-free for many years. Both FRP and PE tanks, however, have a limited life expectancy owing to the corrosive effect of some waste streams. The Hitachi Chemical Co. in Japan has recognized this problem and has developed septic tanks made of thermoset materials having a high corrosion resistance. However, early efforts with the existing thermoset materials for septic tanks resulted in difficult technical problems with molding the tanks into existing tank designs.
A new family of thermoset materials, referred to as RUTENE.TM. polymers, have been developed recently based on polydicyclopentadiene (PDCPD) chemistry. These new polymers solve many of the problems with using thermoset materials for molding septic tanks, and have outstanding corrosion resistance and excellent impact resilience. Osborne Industries, Inc., the assignee of this application, is one of only a few licensees worldwide for these polymers, which have properties similar to thermoplastic polyolefins. RUTENE.TM. is a proprietary name of Osborne Industries, Inc. Existing septic tank designs are not compatible with the preferred molding methods for the RUTENE.TM. polymers.
The strong demand for wastewater treatment facilities of the type pioneered by MicroSepTec has created competitors with nearly equivalent systems. Thus, an improved waste treatment system that can be differentiated from the competition using better technology, such as tanks made with RUTENE.TM. polymers using preferred molding methods, will provide a competitive advantage in this industry.